360 Stock radio off delay after key off

For those of you with the stock radio how long does your radio unit stay on after you turn your key off? I haven't really payed attention to it in the last five years but I noticed yesterday that the radio stayed one for a few seconds and then kind of faded off as if a capacitor was discharging. I have no idea if this is normal but it definitely seemed that having the radio turn off in a uncontrolled way seems out of place for the car.